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MontBell UL Spiral Down Hugger Sleeping Bag Review

A lot to like and a great value for a 30 F rated down mummy bag weighing only 19 ounces.


Overall Rating: Recommended

MontBell’s new Super Spiral Stretch System and soft 12 denier Ballistic Airlight fabric set a new standard for making a lighter sleeping bag. The bag is sized well, has a great fitting hood that is easy to operate, the zipper doesn’t snag, and it’s a great value. The superlatives are offset somewhat by the bag’s only average warmth and a stuff sack that is too small.

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by Will Rietveld |


MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 1
The Spiral Down Hugger #3 introduces MontBell’s new Spiral Stretch System and 12 denier fabric, which together reduce the weight of a sleeping bag by 2 ounces.

Like MontBell’s existing Super Stretch System, their new Super Spiral Stretch System is unique. Basically MontBell found an alternative way to create a stretchy sleeping bag and save some weight to boot. The technology is best described in their own words: “New for 2009, MontBell has incorporated a classic tailor’s technique to address sleeping bag comfort issues. By integrating a woven fabric 'cut on the bias' and orienting the fabric’s warp and weft threads at 45 degrees to major seam lines, the sleeping bag becomes more fluid or elastic in nature. Additionally, 'spring like' crimped fibers are used in the weave of the fabric to capitalize on their inherent stretch properties.” Rather than the traditional horizontal or vertical orientation of the down tubes, they are oriented on a 45 degree angle and appear to spiral around the sleeping bag.

The new Spiral Down Hugger line also introduces MontBell’s new 12 denier Ballistic Airlight sleeping bag fabric. Switching from 15 to 12 denier fabric plus spiral construction reduces the weight of a sleeping bag by about 2 ounces. Apparently MontBell is very satisfied with the new technologies because they intend to extend the Super Spiral Stretch System across their entire sleeping bag line (available March 2010), replacing the current Super Stretch technology.


The main features of Spiral Down Hugger #3, rated at 30 F, are its spiral construction, 12 denier fabric, 800 fill power down, sculptured hood, and three-quarter-length auto-locking zipper. The manufacturer claimed weight is merely 19 ounces for size Regular and 20 ounces for size Long.

My initial reaction to this bag is: “How did they do that?” Frankly, I don’t know, but they did it, and the design works. The 5.5 inch baffled down tubes do not spiral completely around the sleeping bag as the name implies. Rather, the tubes on the top and bottom panels are oriented at a 45 degree angle but run in opposite directions. It would seem like the construction would get complicated at the hood and foot ends of the bag, but MontBell makes it look simple: the spiral construction terminates to a sculptured hood by adding one rounded chamber, and the foot end is neatly finished as well.

I have always been impressed with MontBell’s Ballistic Airlight nylon shell fabrics and Polkatex DWR finish, but the new 12 denier shell on the Spiral Down Hugger is truly remarkable. It’s the softest sleeping bag fabric I have seen, and it sheds water like a duck’s back.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 2
The Spiral Down Hugger’s hood (left) covers the face very well. It draws easily via a simple braided cord and cordlock. On the inside, the bag has a thinly insulated flap that covers the zipper (right), rather than a puffy down-filled draft tube.

The Spiral Down Hugger has a YKK #5CN two-way auto locking zipper, which is used on most lightweight sleeping bags these days. This zipper has separate pulls on the outside and inside of the bag and automatically locks, so it doesn’t open by pulling the sides of the zipper or expanding the bag during the night. To insure that the zipper stays fully zipped, there is a Velcro tab at the top of the zipper, and the Velcro does not stick to the bag’s fabrics.


I tested the Down Hugger #3 on a number of summer and early fall backpacking trips, with nighttime temperatures ranging from 26 to 41 F. I slept under the stars and in various single wall shelters.

MontBell’s sizing is a bit different from other manufacturers; size Regular fits to 5 feet 10 inches and size Long fits to 6 feet 4 inches. I needed a size Long to fit my 6 feet/170 pound frame, and found the fit much to my liking. There is plenty of room inside to wear extra clothing to extend the bag’s warmth, but it didn’t feel too roomy. With the bag lying flat, I measured the bag’s relaxed shoulder girth at 61 inches and extended girth at 72 inches.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 3
The Spiral Down Hugger is indeed stretchy. The left photo shows me lying flat on my back with my arms at my sides; the right photo shows the bag’s expansion with my arms raised above my chest. The benefit of a stretchy bag is the bag tends to conform to my body, so I don’t have to heat up any more inside volume than necessary.

Another remarkable finding from my testing is the bag’s zipper works almost flawlessly, meaning it doesn’t snag very easily. After recently testing a couple of bags with wretched zipper snagging problems (The North Face Beeline and Mountain Hardwear Phantom 32), it’s a pleasure to sleep in the Spiral Down Hugger. (Have you ever had the problem of having an urgent need to pee in the middle of a pitch black night, and the darn zipper snags on your bag?) As shown in the previous section, MontBell uses a thinly insulated flap over the zipper, rather than a puffy insulated draft tube. Eliminating the draft tube allows the zipper to operate more smoothly, but the zipper is not as insulated as it is in other sleeping bags.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 4
I tested the bag’s water repellency by placing a puddle of water on the bag and checking for leakage after an hour. To my amazement no water soaked through. This was verified in my field tests, where the bag did not absorb any water when I brushed against wet tent walls.

I measured the bag’s double layer loft at 3.75 inches, which gives a single layer loft of 1.9 inches. From our table of estimated temperature ratings based on measured loft (read our Backpacking Light Position Statement on Sleeping Bag Temperature Ratings, 1.8 inches of single layer loft translates to about a 30 °F rating, so the Spiral Down Hugger #3 is on target. Please take the time to read the referenced article and note that sleeping bag warmth depends on a number of factors.

The Spiral Down Hugger #3 is not the loftiest bag around with a 30-32 F temperature rating (see comparison table below). I found its warmth to be average. In my field testing, my methodology was to wear my basic sleepwear (dry wool socks and microfleece top, bottom, and cap) inside the bag initially, then add insulated clothing later in the night if I got cold, noting the time and temperature when I got chilly. On nights when the temperature dropped down to freezing just before sunrise, I started getting chilly around 4:00 a.m. when the temperature was around 35 F. After donning my insulated clothing (or better yet putting it on the evening before), I was able to stay warm in the Spiral Down Hugger down to 26 F, and probably could have handled even colder temperatures.

MontBell UL Spiral Down Hugger #3 Sleeping Bag Review - 5
The stuff sack provided is tapered and has two drawcords to stuff the bag down to bread loaf size. It’s simply too tight. In my opinion, the two drawcord design is overkill, extra weight, and overstuffing may damage the down over time. I prefer a stuff sack that does not overstuff a down bag, although it takes up a little more room in my pack.


The following table compares the MontBell UL Spiral Down Hugger #3 with some popular 30-32 F rated ultralight mummy style down sleeping bags. All of the bags have baffled construction, and the data are manufacturer specifications for a size Regular bag.

Manufacturer Model Temperature Rating (F) Single Layer Loft (in) Weight of Down (oz) Fill Power Total Weight (oz) Cost US$
MontBell UL Spiral Down Hugger #3 30 1.9 10 800 19 229
Mountain Hardwear Phantom 32 32 2.0 10 800 22 290
Western Mountaineering SummerLite 32 2.0 10 850+ 19 315
Marmot Hydrogen 30 2.0 11 850+ 25 319
The North Face Beeline 30 2.4 10 850+ 22 279

By the numbers, the MontBell UL Spiral Down Hugger compares favorably with other bags in terms of down quality, weight, and cost. It lags a bit in loft compared to the others, but its loft does meet our minimum expectation of 1.8 inches (single layer) for a 30 F rated sleeping bag. Note that its US$229 cost is a great value compared to the other bags, and its weight matches the Western Mountaineering SummerLite bag.


I really like the Spiral Down Hugger’s soft lightweight shell fabric, fit/roominess, non-snagging zipper, hood, and light weight. It’s very easy to fall in love with this bag, and it’s a great value compared to other ultralight 30 F rated sleeping bags. However, it is not quite as warm as the Mountain Hardwear Phantom 32, and definitely not as warm as the Marmot Hydrogen, which I have also tested. I have not personally tested the Western Mountaineering SummerLite. Bag sizing and the Down Hugger’s lack of a down-filled draft tube probably contribute to the differences. That said, the bottom line for me is to wear my camp clothes (wool socks, insulated jacket and pants, fleece cap) in my sleeping bag anyway, and I typically have no problem staying warm down into the mid 20’s F, so the Spiral Down Hugger #3 will do just fine.

Specifications and Features




2009 UL Spiral Down Hugger #3


Hooded mummy with full length zipper

  What’s Included

Sleeping bag, stuff sack, cotton storage bag


800 fill-power down, 10 oz (283 g) size Regular, 11 oz (312 g) size Long


Box, 5.5 in (14 cm) baffles

  Measured Loft

3.75 in (9.5 cm) average double layer loft, manufacturer specification not available

  Claimed Temperature Rating

30 F (-1 C)

  Stuffed Size

5.3 x 10 in (13.5 x 25 cm)


Size Long tested
Measured weight: 1 lb 4.9 oz (593 g)
Manufacturer specification: 1 lb 4 oz (567 g)


Regular fits to 5 ft 10 in (1.52 m), Long fits to 6 ft 4 in (1.93 m)


Shell and lining are 12d Ballistic Airlight nylon 0.86 oz/yd2 (29 g/m2) with Polkatex DWR. Fibers are solid core.


Spiral stretch system, three-quarter-length two-way auto-locking zipper with inside and outside pulls, draft flap on inside of zipper, Velcro tab at top of zipper, sculptured hood, braided drawcord and cordlock closure on hood, tapered stuff sack with two drawcords, heat transfer logos


Regular US$229
Long US$249


"MontBell UL Spiral Down Hugger Sleeping Bag Review," by Will Rietveld. (ISSN 1537-0364)., 2009-12-08 00:05:00-07.


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MontBell UL Spiral Down Hugger Sleeping Bag Review
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Addie Bedford
(addiebedford) - MLife

Locale: Montana
MontBell UL Spiral Down Hugger Sleeping Bag Review on 12/08/2009 17:15:37 MST Print View

Companion forum thread to:

MontBell UL Spiral Down Hugger Sleeping Bag Review

Kathy A Handyside
(earlymusicus) - M

Locale: Southeastern Michigan
Very Informative Article on 12/08/2009 18:20:10 MST Print View

Thanks for a great article! Very informative. I had already decided to get a Montbell Super Stretch bag anyway. I am a restless side sleeper who sleeps in a fetal position and tosses and turns a lot through the night, so I came to hate mummy bags. I always felt like the bag was holding me hostage, and gave me nightmares of someone coming upon my rigid body, figuring I'd expired, and stuffing me in the ground - or a pyramid! Mont Bell has developed a sleeping bag I can actually sleep in. I've been looking at their bags on their website and liked what I saw. Nice to have my suspicions confirmed!

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
What pad and sleep position is used for your sleeping bag tests? on 12/08/2009 19:32:52 MST Print View


Good job on the review as usual!

Do you use the same sleeping pad to test all of the 30F rated sleeping bags? If so, what is it? What is your primary sleeping position?

Others will experience a significantly different thermal comfort experience if they use a different pad or primary sleep position.

Randy G
(rando3369) - MLife

Locale: Western NY
Great Review, but... on 12/09/2009 04:47:42 MST Print View

I have been checking these out recently also due to the reasonable price. I was all pumped up to by one after reading the great review, but they don't appear to make a 40F rated version like the UL SS Hugger. Maybe in 2010?

Casey Bowden
(clbowden) - MLife

Locale: Berkeley Hills
Re: What pad and sleep position is used for your sleeping bag tests? on 12/09/2009 08:31:43 MST Print View

Richard wrote "Others will experience a significantly different thermal comfort experience if they use a different pad or primary sleep position."

Could you elaborate? Do you know something about this bag not mentioned in the article?

Bradford Rogers
(Mocs123) - MLife

Locale: Southeast Tennessee
Re: Re: What pad and sleep position is used for your sleeping bag tests? on 12/09/2009 09:10:25 MST Print View

It has nothing to do with this particular bag, it is that the pad also plays a large part in keeping you warm and what pad he used can provide additional insight into the warmth of the bag (for example did he use a Thermarest Z-lite with a R value of 2.2 or a Exped Downmat 7 with a R value of 5.9 - big difference) Also sleeping on your side or stomach/back will allow different ratios of body surface contact with the pad (meaning it will have a greater or lesser effect of warmth).

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: What pad and sleep position is used for your sleeping bag tests? on 12/09/2009 11:11:26 MST Print View


I don't know anything about this bag other than what Will discussed. I do know that Will's impression of any sleeping system's lower limit comfort rating will vary significantly based on the sleep position and pad insulation.

If Will slept on his back, then ~35% of the warmth of the MB sleeping bag's sleep system was determined by the pad he used in the test. If the insulation value of the pad was higher than the standard's, then it would bias Will's evaluation towards the bag being warmer than an EN 13537 LLimit comfort rating. If the insulation value of the pad was lower than the standards, then it would bias Will's evaluation towards the MB bag being colder. If Will slept primarily on his side then ~ 18% of the warmth of the sleep system was primarily determined by the pad.

In order for Will's field test LLimit comfort rating to correlate with an accurate EN 13537 LLimit rating of a bag, Will would have to have slept on his side and used a pad with an R Value of 4.85.

Loft vs warmth

Two of the bags, used in Will’s 30F rated bags comparison table, (MH Phantom & Marmot Hydrogen) have been EN 13537 laboratory tested using the standard side sleep position and 4.85 pad insulation value.

Edited by richard295 on 12/10/2009 17:20:56 MST.

Mitchell Keil
(mitchellkeil) - F

Locale: Deep in the OC
Re: MontBell UL Spiral Down Hugger Sleeping Bag Review on 12/09/2009 13:55:46 MST Print View

I have owned several of the MBSS bags and have also been impressed with their comfort and true temp ratings. I note that you have two pictures of yourself in the bag: one, sans tent and the other inside the tent. WHen you comment on a bag are you commenting from the perspective of being exposed to the elements or not. Convection can rob a bag of a lot of warmth, so I was just wondering how you tested the bag's warmth. I wish all of you who test bags would let us know this kind of info when reviewing. It does make a difference. thanks and a great review as always.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Re: MontBell UL Spiral Down Hugger Sleeping Bag Review on 12/09/2009 15:47:46 MST Print View


Great point about the benefit of also defining the shelter(s) used for an evaluation!

In addition to the convection variable there can be a significant IR variable. When sleeping under the stars, on a clear night, the IR exchange will reduce the surface of a sleeping bag significantly below the ambient air temperature. Tree cover is also an important IR related variables.

Kendall Clement
(socalpacker) - MLife

Locale: Southern California
Re: MontBell UL Spiral Down Hugger Sleeping Bag Review on 12/09/2009 15:49:02 MST Print View

Thanks Will! That was really great! Your reviews are very informative and thorough and I look forward to each one. Thanks again.

Edited by socalpacker on 12/09/2009 15:49:44 MST.

Patricia Combee
(Trailfrog) - F

Locale: Northeast/Southeast your call
RE: Montbell spiral down hugger on 12/09/2009 17:42:05 MST Print View

I bought one of these bags this spring. Very nice bag. Warm enough, nice fit.
Thanks for the nice review. I always wondered about the water repellancy of the bag but was too chicken to intentionally get it wet. It was nice of you to test that part out.

Larry Risch
(dayhiker) - F
Typo? on 12/09/2009 20:36:50 MST Print View


No reason to make people read it anymore.

Edited by dayhiker on 12/09/2009 21:26:49 MST.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Typo? on 12/09/2009 20:56:20 MST Print View


You are right, it was a typo that is now corrected. Thank you for diplomatically pointing it out.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Loft Correlation with Laboratory Measured Insulation Values on 12/10/2009 17:34:45 MST Print View

Marmot Customer Service measured the loft of their two 30F synthetic bags for me. I added the data for these two 30F marketed synthetic bags to Will's table in my original post to this thread.

Will Rietveld
(WilliWabbit) - MLife

Locale: Southwest Colorado
Re: What pad and sleep position is used for your sleeping bag tests? on 12/10/2009 18:16:42 MST Print View

Hi Everyone,

I used a Big Agnes Clearview pad for testing the Spiral Down Hugger. Most of my testing was done in the summer and early fall, so the Clearview was warm enough underneath. I'm a side sleeper. I slept in either a solo single wall tent (BSI Mirage 1P) or under the stars.


Jim MacDiarmid
(jrmacd) - MLife
Re: MontBell UL Spiral Down Hugger Sleeping Bag Review on 12/10/2009 20:28:20 MST Print View

I owned both the MB Spiral Down #3 and the WM Summerlite at the same time while trying to find a 3 season Sierra area sleeping bag.

I concur with Will's finding regarding the MB bag, and felt the Summerlite was warmer. I was able to use both bags on consecutive nights in Little Yosemite Valley in 40 degree temps. The 1st night, I used the summerlite under a tarp, inside a Tigoat bivy, on a GG 1/8" thinlite under a short NeoAir. I woke up and had to fully unzip and quilt the summerlite to regulate my temperature.

2nd night I used the MB in a Tarptent Rainbow, on the same pad system, minus the Bivy(I was testing new stuff) I was just comfortable. Not too warm, not too cold.

I also used the MB on Mt Shasta, on snow in June, in temps that touched freezing. I slept both exposed in just a bivy, on the thinlite plus NeoAir, and also in a the TT Rainbow, in the bivy + pads. My feet got cold, and I added my MB UL Down Inner parka, but I believe I was cold mainly due to my inadequate pad combination, only R-value 3 on frozen ground.

While the Summerlite was definitely the warmer of the two, I would have chosen the MB due to the spacious interior. I'm a 3/4 stomach/side sleeper that moves around a bit in my sleep. The Summerlite had just enough room, but the MB was perfect.

I also prefered the feel of the MB fabric, which has a bit of texture, vs the slick microlight WM fabric.

I got a Nunatak Arc Specialist on gear swap, which superceded both those bags.

alice fogel
Re: Great Review, but... on 12/23/2009 08:16:46 MST Print View

Also, what about a smaller (women's) size? Is there any plan to have this in 2010?

Dave Master
(dave_master_edu) - M
MontBell SuperStretch Bag on 01/01/2010 20:21:40 MST Print View

I bought a MontBell SuperStretch bag this year and used late summer in Mineral King (Sequoia-Kings Canyon). It's the best bag I've ever owned! I've had other bags that kept me just as warm, but I toss and turn a lot in my sleep. Every other bag I've owned felt like I was in a straitjacket. This is the first bag I've owned that allowed be to sleep through the night just as comfortably as if I were in my own bed!

Frank Steele
(knarfster) - F

Locale: Arizona
Mont-Bell #3 sent back on 03/14/2010 23:31:46 MDT Print View

I purchased a Mont-Bell Spiral Down Hugger #3 for myself and a Sierra Designs Nitro 30 for my Son (12 year old boy scout only 3 inches shorter than, he is 5' 4"). The Nitro was on sale at Moontrail for only $189 (should have bought 2!)

I love the stretch of the #3, but I sleep cold so on a night at 38-40 Degrees I was cold even in my old Poly pros. My Son said he was toasty warm in his bag. I tried the Nitro 30 and it was indeed warm, but too tight for me, if I had to wear my Mont-Bell thermawrap I would be squeezed.

I sent the Spiral DH #3 bag and I am getting a UL Super Stretch #2, which weighs 28 oz, but has 14 oz of Down. I am hoping it is much warmer, as I do not want to spend the money on a Nunutak Alpinist just yet> I have invested in Ibex tops and botttoms too. I can live with the heavier bag (9 oz more than a Spiral DH and 3 oz more than the Nitro 30). I wish they made a Spiral DH #2 with 14 oz of Down, it would still only weigh 23 oz! Oh well.

If you sleep warm, the Spiral Down Hugger #3 may be for you. I think I need a #2, if that doesn't work, I will try a Spiral Down Hugger #1, which has 20 oz of Down and weighs 2 lbs., that should be plenty warm.

Edited by knarfster on 03/14/2010 23:34:01 MDT.

jimmy benson
(biggyshorty) - F
pack weight? on 07/11/2010 15:13:25 MDT Print View

hi, long time lurker and new poster -

does anyone know how far down the #3 will pack? i'm thinking an outdoor research silnyl 10L bag, but is that too small?